VPA was recently classified among the Histone Deacetylase (HDAC) inhibitors, acting directly at the level of gene transcription by inhibiting histone deacetylation and making transcription sites more accessible. Chromatin is formed of DNA packaged in nucleosome structures. The condensed form of chromatin (heterochromatin) is inactive in terms of transcription whereas the decondensed form (euchromatin) corresponds to an active form. The histone acetylation leads to relaxation of the nucleosome structure, releasing the DNA and allowing transcription. Inhibition of histone deacetylases (HDACs) promotes decondensed chromatin formation, thereby promoting the expression of genes (7).